A singleton ActionCable::Server instance is
available via ActionCable.server. It's used by the Rack process that
starts the Action Cable server, but is also used by the user to reach the
RemoteConnections object, which is
used for finding and disconnecting connections across all servers.

Also, this is the server instance used for broadcasting. See Broadcasting for more information.

The worker pool is where we run connection callbacks and channel actions.
We do as little as possible on the server's main thread. The worker
pool is an executor service that's backed by a pool of threads working
from a task queue. The thread pool size maxes out at 4 worker threads by
default. Tune the size yourself with
config.action_cable.worker_pool_size.

Also, ensure that your database connection pool size is as least as large
as your worker pool size. Otherwise, workers may oversubscribe the database
connection pool and block while they wait for other workers to release
their connections. Use a smaller worker pool or a larger database
connection pool instead.